Purpose: Consecutive exotropia is a frequent consequence of surgery for convergent strabismus that may develop at differing rates postoperatively. Several surgical options on horizontal recti have been proposed, but none report a clearly standardized amount of surgery. The present study provides further results of the medial rectus muscle advancement. Methods: Twenty-eight patients, age range 6 - 55 years, who had undergone unilateral or bilateral medial rectus advancement to the physiological insertion, with or without contemporary unilateral lateral rectus muscle recession, were included in the study. Factors leading to the onset of consecutive exotropia were analyzed. Results: After 2 - 3 years, the overall mean angle reduction was 21.3 prismatic diopters (PD) for distance and 22.8 PD for near, with an effectiveness on near vision lower than expected. Only in the 7 cases with a preoperatively larger exotropia at near (of at least 10 PD), the reduction was 17.0 PD for distance and 24.6 PD for near. In unilateral medial rectus muscle advancement, the mean reduction was 14.3 PD for distance and 16.3 PD for near; in bilateral advancement it was 25.8 PD and 25.2 PD respectively. Conclusion: Medial rectus advancement is preferable to other options, especially in cases with convergence deficit, if no excess of divergence or limitation of bulb rotation is present, for which a lateral rectus muscle recession is indicated. Unilateral and bilateral surgeries are useful for exotropia of about 15 PD and 25 PD respectively. The effectiveness depends weakly or not at all by the amount of the previously executed recession.
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